Financial Instruments and Fair Value Measurements - Carrying Amount and Fair Value (Details) - Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Carrying Value
Financial instruments and fair value measurements
Debt	$ 448,458	$ 459,221
Fair Value
Financial instruments and fair value measurements
Debt	407,933	412,259
Level 1 | Carrying Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,119	3,824
Level 1 | Fair Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,093	3,750
Level 2 | Carrying Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	259,278	262,484
Level 2 | Carrying Value | Variable rate debt
Financial instruments and fair value measurements
Debt	189,180	196,737
Level 2 | Fair Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	218,753	215,522
Level 2 | Fair Value | Variable rate debt
Financial instruments and fair value measurements
Debt	189,180	196,737
Level 3 | Carrying Value
Financial instruments and fair value measurements
Senior Notes held by SPE	178,402	178,162
Level 3 | Carrying Value | Time deposit
Financial instruments and fair value measurements
Investments held by SPEs	200,000	200,000
Level 3 | Fair Value
Financial instruments and fair value measurements
Senior Notes held by SPE	183,201	181,286
Level 3 | Fair Value | Time deposit
Financial instruments and fair value measurements
Investments held by SPEs	$ 200,000	$ 200,000